摘要:

Heart rate was controlled by direct stimulation of the right ventricle of a dog previously subjected to complete A-V block in order to study the effect of this variable on cardiac output. Measurements of cardiac output were made at various heart rates in unanesthetized dogs, both at rest and walking on a treadmill. Except at the extremes, cardiac output was independent of heart rate at rest and during mild exercise. This finding emphasizes the fact that cardiac output may be regulated to provide required flow through changes in stroke volume alone, even though adjustment of heart rate is the usual means for obtaining this end.

ISSN:0009-7330    

出版商:OVID    

年代:1960

数据来源: OVID

摘要:

Between 37 and 20 C., the resting potential of sheep ventricular and Purkinje fibers was found to be proportional to the absolute temperature. Prom 20 to 0 C., the potential drop was 3 times greater than that predicted from the theory of a concentration potential. Rapid heating by high-frequency current of previously cooled preparations, revealed no time lag between the rise of potential and the rise of temperature. Fibers kept in a Na-free solution still showed a large temperature sensitivity. With poisoned fibers, the resting potential was almost proportional to the absolute temperature. The results appear to contradict the hypothesis that extracellular K accumulation in the cold is the cause of the potential drop. They also exclude the hypothesis that a relative rise of the Na-inward current is the reason for depolarization. They support the idea that “active” extrusion of Na ions normally contributes to the resting potential, and that the pumping rate decreases considerably in the cold.

ISSN:0009-7330    

出版商:OVID    

年代:1960

数据来源: OVID

摘要:

Measurements of stroke volume were made in dogs during graded exercise on a horizontal treadmill up to the maximal exercise which they could maintain for 2 to 3 minutes. Eleven series of experiments were performed on 7 dogs. The cardiac output was measured by the indicator-dilution technic and the heart rate was measured from the aortic pressure tracing. At all grades of exercise, there was little or no change in stroke volume. Even with severe exercise, when the cardiac output had increased from 1.5 to 3.5 (average, 2.4) times the values obtained with the dog standing at rest, the stroke volume showed less than 5 per cent change over resting values in 5 experiments on 4 dogs, while in the remainder the increases were 8, 11, 11, 14, 15, and 19 per cent. Thus, the increase in cardiac output in the untrained exercising dog is almost directly proportional to the increase in heart rate. This is in contrast to other situations, such as the combination of exercise with infusion of catecholamines, where an increase in stroke volume may make an important contribution to the increase in cardiac output.

ISSN:0009-7330    

出版商:OVID    

年代:1960

数据来源: OVID

摘要:

The response of the adrenal medulla in anesthetized dogs to hemorrhagic hypotension of a varied level and duration was observed to be primarily accompanied by a highly significant increase in adrenal plasma epinephrine. On the other hand, the secretion of norepinephrine had an unpredictable occurrence in adrenal blood samples collected in periods of hypotension. The essential determinant of adrenal blood flow was observed to be the level of mean blood pressure. While this relationship was not in strict proportion, changes in mean blood pressure were invariably followed by changes in adrenal blood flow in the same direction. The adrenal medulla of dogs in hemorrhagic irreversible shock was observed to continue to secrete epinephrine at very low levels of mean blood pressure, characteristic of terminal shock. Reports by other groups of investigators on elevated peripheral blood levels of epinephrine in hemorrhagic shock have been found to result mainly from an actively secreting adrenal medulla.

ISSN:0009-7330    

出版商:OVID    

年代:1960

数据来源: OVID

摘要:

Insulin administration to intact cockerels made atherosclerotic by the feeding of a cholesterol-oil-containing diet prevented regression of coronary atherosclerosis. Insulin administration during the induction of atherosclerosis had no effect on the development of lesions. In some experiments, insulin slightly inhibited estrogen-induced protection of the coronary arteries when the birds were on a high cholesterol-oil diet.

ISSN:0009-7330    

出版商:OVID    

年代:1960

数据来源: OVID

摘要:

The results of a study of the sealar electrocardiogram, utilizing a wide-band recorder, expanded time scale and a low-pass filter, indicate that a recorder flat to at least 500 c.p.s. is required for faithful reproduction. With a high-pass filter, measurable residual signals are present at a cut-off frequency of 1,000 c.p.s., or higher. Therefore, to record these, an adequate response at 1,000 c.p.s. or more is reqnired. The high frequency energy of the electrocardiographic spectrum arises from the fast deflections contained in the original waveform. These may occur in a single fast deflection, notching, or both. Whereas, in the normal individual, high frequency energy usually arises from a relatively smooth, fast deflection, in abnormals the fast events may occur in conjunction with notching, and other deformities. Judging from the technic used in this experiment, a variable band-pass filter is valuable as an aid for studying the high frequency components of the electrocardiogram and establishing equipment requirements. Measurement of peak-to-peak voltage of residual signals gives partial but lot clear-cut separation of normal and abnormal subjects and would not seem to add to the value of high-fidelity electrocardiography per se in routine clinical diagnosis. It is possible that root mean square readings, reflecting the total energy content, might give a better separation between normal and abnormal subjects than peak-to-peak amplitude alone.

ISSN:0009-7330    

出版商:OVID    

年代:1960

数据来源: OVID

摘要:

In anesthetized dogs, the inhalation of 5 per cent oxygen caused vasoconstriction of perfused hind limb but vasodilatation occurred during reoxygenation. The vasoconstriction during anoxia amounted to a mean increase of vascular resistance of +12 per cent if blood from the same anoxic dog was used for perfusion, and to +35 per cent if blood from a nonanoxic donor was used. This vasoconstrictor response was almost entirely the outcome of anoxemic stimulation of chemoreceptors in the carotid and aortic bodies. The vasodilatation during reoxygenation persisted after chemoreceptor denervation, but was eliminated by either spinal cord transection or denervation of the limb. The nervous pathways responsible for this postanoxic vasodilatation were resistant to bretylium but were partially blocked by either atropine or hexamethonium.

ISSN:0009-7330    

出版商:OVID    

年代:1960

数据来源: OVID

摘要:

Volume-pressure curves were determined for the living left heart vascular segment by injecting fluid into the left atrium during momentary cardiac asystole and measuring left atrial pressure. Such curves show 2 essentially linear relationships with a break at a low pressure level. It has been suggested that this break is due to closure of the pulmonary veins or the pulmonary-left atrial junction at low pressure levels. This closure prevents regurgitation into the pulmonary veins. Higher atrial pressures overcome this block and permit retrograde perfusion of the pulmonary pathways. This suggestion was tested by measuring left atrial and pulmonary vein pressure during the injection of blood into the atrium of the quiescent heart. The results are consistent with such a collapse of the veno-left atrial junction at low pressure levels.

ISSN:0009-7330    

出版商:OVID    

年代:1960

数据来源: OVID

摘要:

By applying microelectrode technic in isolated dog hearts, the nature of the so-called unidirectional conduction of the atrioventricular conduction was investigated. Retrograde conduction, i.e., conduction from the ventricle, occurred frequently in the isolated whole heart from which the sinus node was removed, or in a preparation composed of the interatrial septum, right atrium, right ventricle, interventricular septum, and atrioventricular conduction system. Retrograde conduction was blocked just as frequently. In such cases, this unidirectional block was found not to be ascribed solely to the refractory period of the atrioventricular node or of the atrial muscle fibers. The site of unidirectional block was found to be located in the domain of the ventricle, i.e., in the region adjacent to the postero-inferior margin of the membranous portion of the interventricular septum. This site is of a very limited extension. This point responded to ventricular stimuli, frequently by localized depolarization only, or in the manner of decremental conduction, whereas following atrial stimuli, it responded with full-sized action potential. By histologic examination, it was found that this point is situated in the ventricular portion of the bundle of His, just above the bifurcating point to the right and left branches.

ISSN:0009-7330    

出版商:OVID    

年代:1960

数据来源: OVID

摘要:

Partial heart-lung bypass was performed in open-chest dogs, using the gravity arterial in-fusion technique. Arterial infusion pressure, venous suction and pressures in the left ventricle, aortic arch, and airways were phasically recorded. The mean flow in the aortic arch and the blood content of the extracorporeal circuit were continuously recorded. According to the height of the bag oxygenator above the heart level, partial heart-lung bypass resulted in a shift of blood either from the extracorporeal circuit into the animal or vice versa. When the body blood volume was increased by the bypass procedure, the cardiac output decreased only slightly. When the body blood volume was diminished by the bypass procedure, the cardiac output dropped markedly. It was found that when the systemic arterial pressure was maintained at approximately normal levels, independent of cardiac output, the change in cardiac output was proportional to the change in the body blood volume.

ISSN:0009-7330    

出版商:OVID    

年代:1960

数据来源: OVID